Transport Across Cell Membranes (3.2.3) Flashcards
What does the cell-surface membrane do?
- Acts as a barrier as it controls what enters and exits the cell
Why is the structure of the cell-surface membrane described as a fluid mosaic model?
- The phospholipid molecules are constantly moving about giving a fluid structure
- Many different protein molecules are unevenly distributed throughout the membrane forming a mosaic
Depending on the number of saturated or unsaturated fatty acids in the phospholipid bilayer how does the permeability change?
- More saturated fatty acids → permeability is decreased
- More unsaturated fatty acids → permeability is increased.
What movement does the phospholipid bilayer allow for and what does it prevent?
- Allows for the movement of non-polar or very small molecules
- Prevents the movement of polar or large molecules
What structures are embedded in the phospholipid bilayer of the cell-surface membrane?
- Cholesterol
- Carrier proteins
- Channel proteins
- Intrinsic proteins
- Extrinsic proteins
- Glycolipids
- Glycoproteins
What does cholesterol do?
- Provides strength to the membrane by restricting phospholipid movement, reducing permeability and reducing ion loss
What do carrier proteins do?
- Aid the transport of polar molecules such as glucose or amino acids by facilitated diffusion or active transport
What do channel proteins do?
- Aid the transport of molecules or ions across the membrane by facilitated diffusion
What are glycolipids, and what is their function?
- Lipids attached to carbohydrate chains
- Involved in cell recognition
What are glycoproteins, and what is their function?
- Proteins attached to carbohydrate chains
- Function as cell surface receptors
What is equilibrium?
- When molecules are equally distributed and there is no net movement in either direction
What is diffusion?
- The net movement of molecules from an area of high concentration to an area of low concentration until equilibrium is reached
What is facilitated diffusion?
- The movement of molecules from an area of high concentration to an area of low concentration across a partially permeable membrane requiring channel or carrier proteins
What can cause the rate of facilitated diffusion to plateau?
- It levels off because it’s limited by all the channel or carrier proteins being saturated
What are the factors affecting the rate of movement across a membrane?
- Temperature → higher temperatures increase the kinetic energy of the molecules, causing them to move faster and thus diffuse more rapidly
- Surface area → a greater surface area provides more space for molecules to pass through, speeding up the rate of diffusion
- Concentration gradient → a steeper concentration gradient, a larger difference in the concentrations inside and outside of the cell, results in faster diffusion
What is active transport?
- The movement of molecules from an area of low concentration to an area of high concentration, against the concentration gradient across a partially permeable membrane
- This process requires energy from the hydrolysis of ATP and is facilitated by carrier proteins
What factors affect the rate of active transport?
- Temperature → higher temperatures increase the kinetic energy of the molecules, causing them to move faster and thus increasing the rate of active transport
- Levels of oxygen → increased levels of oxygen increases the amount of ATP produced in respiration, which in turn increases the rate of active transport
- Presence of metabolic and respiratory inhibitors → metabolic and respiratory inhibitors block respiration, reducing ATP production and stopping active transport
What is osmosis?
- The net movement of water molecules from an area of higher water potential to an area of lower water potential across a partially permeable membrane
